Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time - Dava Sobel (2005)

Chapter 11. Trial by Fire and Water

Two lunar months are past, and more,

Since of these heroes half a score

Set out to try their strength and skill,

And fairly start for Flamsteed-Hill …

But take care, Rev. M-sk-l-n,

Thou scientific harlequin,

Nor think, by jockeying, to win …

For the great donor of the prize

Is just, as Jove who rules the skies.

—“C.P.” “Greenwich Hoy!” or “The Astronomical Racers”

A story that hails a hero must also hiss at a villain—in this case, the Reverend Nevil Maskelyne, remembered by history as “the seaman’s astronomer.”

In all fairness, Maskelyne is more an antihero than a villain, probably more hardheaded than hardhearted. But John Harrison hated him with a passion, and with good reason. The tension between these two men turned the last stretch of the quest for the longitude prize into a pitched battle.

Maskelyne took up, then embraced, then came to personify the lunar distance method. The man and the method melded easily, for Maskelyne, who put off marrying until he was fifty-two, enslaved himself to accurate observation and careful calculation. He kept records of everything, from astronomical positions to events in his personal life (including each expenditure, large or small, over the course of four-score years), and noted them all with the same detached matter-of-factness. He even wrote his own autobiography in the third person: “Dr. M.,” this surviving handwritten volume begins, “is the last male heir of an ancient family long settled at Purton in the County of Wilts.” On subsequent pages, Maskelyne refers to himself alternately as “he” and “Our Astronomer”— even before his main character becomes astronomer royal in 1765.

The fourth in a long line of Nevils, Maskelyne was born on October 5, 1732. This made him about forty years younger than John Harrison, although he seemed never to have been young. Described by a biographer early on as “rather a swot” and “a bit of a prig,” he threw himself into the study of astronomy and optics with every intention of becoming an important scientist. Family letters refer to his older brothers, William and Edmund, as “Billy” and “Mun,” and call his younger sister, Margaret, “Peggy,” but Nevil was always and only Nevil.

Unlike John Harrison, who had no formal education, Nevil Maskelyne attended Westminster School and Cambridge University. He worked his way through college, performing menial tasks in exchange for reduced tuition. As a fellow of Trinity College, he also took holy orders, which earned him the title of Reverend, and he served for a while as curate of the church at Chipping Barnet, roughly ten miles north of London. Sometime in the 1750s, while Maskelyne was still a student, his lifelong devotion to astronomy and his Cambridge connections brought him into the company of James Bradley, the third astronomer royal. They made a natural pair, and mated their two true methodical minds for life, in joint pursuit of a longitude solution.

Bradley, at this point in his career, was on the verge of codifying the lunar distance method with the help of the tables sent over from Germany by the astronomer-mathematician-mapmaker Tobias Mayer. Between 1755 and 1760, according to Maskelyne’s account of the story, Bradley undertook 1,200 observations at Greenwich, followed by “laborious calculations” comparing them to Mayer’s predictions, in an effort to verify the tables.

Maskelyne naturally took an interest in these matters. In 1761, on the occasion of the much-heralded astronomical event called the transit of Venus, Maskelyne won from Bradley a plum position on an expedition to prove the validity of Mayer’s work—and to demonstrate the value of the tables for navigation.

Maskelyne voyaged to the tiny island of St. Helena, south of the Atlantic Equator, where Edmond Halley had journeyed in the previous century to map the southern stars, and where Napoleon Bonaparte would be condemned, in the following century, to live out his last days. Sailing to and from St. Helena, Maskelyne used Hadley’s quadrant and Mayer’s tables to find his longitude at sea, many times over, much to his and Bradley’s delight. The lunar distance technique worked like a charm in Maskelyne’s able hands.

Maskelyne also used lunar distances to establish the precise longitude of St. Helena, which had not been known before.

During his sojourn on the island, Maskelyne carried out what was ostensibly his primary mission: He watched over a period of hours as the planet Venus moved, like a small, dark blemish, across the sun’s face. In order for Venus to transit, or trespass in this fashion, the planet must pass precisely between the Earth and the sun. Because of the relative positions and paths of the three bodies, transits of Venus come in pairs, one transit eight years after the other—but only a single pair per century.

Halley had witnessed part of a more common transit of Mercury from St. Helena in 1677. Very excited about the possibilities of such occurrences, he urged the Royal Society to track the next transit of Venus, which, like the return of Halley’s comet, he could not possibly live long enough to see firsthand. Halley argued convincingly that lots of careful observations of the transit, taken from widely separated points on the globe, would reveal the actual distance between the Earth and the sun.

Thus, Maskelyne set out for St. Helena in January 1761 as part of a small but global scientific armada, which included numerous French astronomical excursions to carefully selected observing sites in Siberia, India, and South Africa. The June 6, 1761, transit of Venus also paired (Charles) Mason with (Jeremiah) Dixon on a successful observing run at the Cape of Good Hope—several years before the two British astronomers drew their famous boundary line between Pennsylvania and Maryland. The second transit, predicted for June 3, 1769, launched the first voyage of Captain James Cook, who proposed to view the event from Polynesia.

Maskelyne discovered that the weather at St. Helena, unfortunately, had not improved much since Halley’s visit, and he missed the end of the transit behind a cloud. Nevertheless, he stayed on for many months, comparing the force of gravity at St. Helena with that at Greenwich, trying to measure the distance to the nearby bright star Sirius, and using observations of the moon to gauge the size of the Earth. This work, coupled with his prowess on the longitude frontier, more than made up for his problems in viewing Venus.

Meanwhile, another voyage of monumental importance to the longitude story, though altogether unrelated to the transit expeditions, also set sail in 1761, when William Harrison carried his father’s watch on a sea trial to Jamaica.

Harrison’s first timekeeper, H-1, had ventured only as far as Lisbon, Portugal, and H-2 had never gone to sea at all. H-3, almost twenty years in the making, might have been tried on the ocean immediately upon its completion in 1759 but for the inconvenience of the Seven Years War. This worldwide war spanned three continents, including North America, as it brought England, France, Russia, and Prussia, among other countries, into its fray. During the turmoil, Astronomer Royal Bradley had tested written copies of the lunar distance tables aboard warships patrolling the enemy coast of France. No one in his right mind, however, would send a one-of-a-kind instrument like H-3 into such troubled waters, where it might be captured by hostile forces. At least that was the argument Bradley gave in the beginning. But the argument fell apart in 1761, when the official trial of H-3 finally came up—despite the fact that the great war still raged, having progressed through only five of its eponymous seven years. It’s irresistible to imagine that, by then, Bradley wanted something bad to happen to H-3. In any case, the international drive to pursue the transit of Venus must somehow have legitimized all voyages flying under the flag of science.

Between the completion and the trial date of H-3, Harrison had proudly presented his pièce de résistance, H-4, to the Board of Longitude in the summer of 1760. The Board opted to test both H-3 and H-4 together on the same voyage. Accordingly, in May of 1761, William Harrison sailed with the heavy sea clock, H-3, from London to the port of Portsmouth, where he had orders to wait for a ship assignment. John Harrison, fussing and fine-tuning H-4 till the very last minute, planned to meet William at Portsmouth and deliver the portable timekeeper into his hands just before the ship weighed anchor.

Five months later, William was still on the dock in Portsmouth, waiting for his sailing orders. It was now October, and William fretted with frustration over the delayed trial and fear for the health of his wife, Elizabeth, still ill after the birth of their son, John.

William suspected that Dr. Bradley had deliberately delayed the trial for his personal gain. By holding up the Harrison trial, Bradley could buy time for Maskelyne to produce proof positive supporting the lunar distance method. This may sound like a paranoid delusion on William’s part, but he had evidence of Bradley’s own interest in the longitude prize. In a diary, William had recorded how he and his father chanced to encounter Dr. Bradley at an instrument-maker’s shop, where they incurred his obvious antagonism: “The Doctor seemed very much out of temper,” noted William, “and in the greatest passion told Mr. Harrison that if it had not been for him and his plaguey watch, Mr. Mayer and he should have shared Ten Thousand Pounds before now.”

As astronomer royal, Bradley served on the Board of Longitude, and was therefore a judge in the contest for the longitude prize. This description of William’s makes it sound as though Bradley himself was also a contender for the prize. Bradley’s personal investment in the lunar distance method could be called a “conflict of interest,” except that the term seems too weak to define what the Harrisons stood up against.

Whatever the cause of the delay, the Board convened to take action shortly after William returned to London in October, and November saw him embarked at last on H.M.S. Deptford. With H-4 alone. During the long predeparture delay, his father had seen fit to remove H-3 from the running. The Harrisons were banking everything on the Watch.

The board insisted, as a means of quality control over the trial, that the box containing H-4 be fitted with four locks, each opening to a different key. William got one of the keys, of course, for he had charge of the daily winding. The other three went to trusted men willing to witness William’s every move— William Lyttleton, then governor-designate of Jamaica and William’s fellow passenger aboard the Deptford, the ship’s captain, Dudley Digges, and Digges’s first lieutenant, J. Seward.

Two astronomers, one in Portsmouth and another one sailing along to Jamaica, took charge of establishing the correct local time of departure and arrival. William was required to set the Watch by them.

On the very first leg of the journey, much cheese and many whole barrels of drink were found unfit for consumption. Captain Digges ordered them thrown overboard, precipitating a crisis. “This day,” reads a note in the journal of the ship’s master, “all the Beer was expended, the People oblidged to drink water.” William promised a speedy end to the distress, as he reckoned with H-4 that the Deptford would make Madeira within a day. Digges argued that the Watch was way off, as was the island, and offered to lay odds on the bet. Regardless, the next morning brought Madeira into sight—and fresh barrels of wine into the hold. At this juncture, Digges made Harrison a new offer: He would buy the first longitude timekeeper that William and his father put up for sale, the moment it became available. While still in Madeira, Digges wrote to John Harrison:

“Dear Sir, I have just time to acquaint you … of the great perfection of your watch in making the island on the Meridian; According to our Log we were 1 degree 27 minutes to the Eastward, this I made by a French map which lays down the longitude of Teneriffe, therefore I think your watch must be right. Adieu.”

The Atlantic crossing took nearly three months. When the Deptford arrived at Port Royal, Jamaica, on January 19, 1762, the Board’s representative John Robison set up his astronomical instruments and established local noon. Robison and Harrison then synchronized their watches to fix the longitude of Port Royal by the time difference between them. H-4 had lost only five seconds—after 81 days at sea!

Captain Digges, a great one for giving credit where it was due, ceremonially presented William— and his father, in absentia—with an octant to commemorate the successful trial. Curators at the National Maritime Museum, where this particular trophy-instrument is now displayed, note on a comment card that it seems “an odd present, perhaps, for someone trying to make the Lunar-Distance Method of determining Longitude redundant.” It must be the case that Captain Digges had seen a bullfight somewhere, and by this gesture he was awarding William the ears and tail of the vanquished animal. What’s more, even with the Watch in hand to tell the time in London, Digges would still need his octant to establish local time at sea.

A little over a week after they reached Jamaica, William, Robison, and the Watch went back to England aboard the Merlin. With worse weather on the return, William worried constantly about keeping H-4 dry. The rough seas leapt onto the ship, often submerging the decks under two feet of water and leaking a good six inches into the captain’s cabin. Here poor seasick William wrapped the Watch in a blanket for protection, and when the blanket got soaked, he slept in it to dry the cloth with his body heat. William ran a raging fever by the end of the voyage, thanks to these precautions, but felt vindicated by the result. Upon its arrival home on March 26, H-4 was still ticking. And its adjusted total error, outbound and homebound combined, amounted to just under two minutes.

The prize should have gone to John Harrison then and there, for his Watch had done all that the Longitude Act demanded, but events conspired against him and withheld the funds from his deserving hands.

First there was the evaluation of the trial, which came up at the next meeting of the Board of Longitude, in June. Having stipulated the four keys and the two astronomers, the board now called for three mathematicians to check and recheck the data on the time determinations at Portsmouth and Jamaica, as both of these suddenly seemed insufficient and inaccurate. The commissioners also complained that William had failed to follow certain rules set down by the Royal Society for establishing the longitude at Jamaica by the eclipses of Jupiter’s moons—something William didn’t realize he was required to do, and wouldn’t have known how to do in any case.

Therefore, the board concluded in its final report in August 1762, “the Experiments already made of the Watch have not been sufficient to determine the Longitude at Sea.” H-4 must needs submit to a new trial, under stricter scrutiny. Back to the West Indies with it, and better luck next time.

Instead of £20,000, John Harrison received £1,500, in recognition of the fact that his Watch “tho’ not yet found to be of such great use for discovering the Longitude … is nevertheless an invention of considerable utility to the Public.” He could expect another £1,000 when H-4 returned from its second stint at sea.

Maskelyne, defender of the rival method, had arrived back in London from St. Helena in May 1762, hot on William’s heels, and quite flush with accomplishment. He immediately cemented his future reputation by publishing The British Mariner’s Guide—an English translation of Mayer’s tables, plus directions for their use.

Mayer himself had died in February, at thirty-nine, the victim of a virulent infection. Then Bradley, the astronomer royal, died in July. His death, at sixty-nine, may have seemed less premature, though Maskelyne swore his mentor’s life had been unduly shortened by hard labor on the lunar tables.

The Harrisons discovered immediately that the loss of Bradley from the Board of Longitude offered no reprieve. His death failed to soften the hard-nosed attitude of the other commissioners. All that summer, as the post of astronomer royal fell vacant and then was filled through the appointment of Nathaniel Bliss, William corresponded with the board members to vindicate the Watch. He took hard knocks at two board meetings in June and August, and carried the discouraging words home to his father.

As soon as Bliss took his ex officio seat on the Board of Longitude as the fourth astronomer royal, he took aim at the Harrisons. Like Bradley before him, Bliss was all for lunars. He insisted that the Watch’s so-called accuracy was a mere chance occurrence, and he did not predict a precision performance on the next trial.

None of the astronomers or admirals on the board had any knowledge about the Watch or what made it run so regularly. They may have been incapable of understanding its mechanism, but they began hounding Harrison early in 1763 to explain it to them. This was a matter of both intellectual curiosity and national security. The Watch had value, for it seemed an improvement over the ordinary watches used to time the taking of lunars. The Watch might even stand in for the lunars in foul weather, when the moon and stars disappeared. Then, too, John Harrison wasn’t getting any younger. What if he died and took the potentially useful secret to the grave with him? What if William and the Watch went down together in some nautical disaster on the next trial? Clearly, the board needed a full disclosure on the timekeeper before they sent it back to sea.

The French government dispatched a small contingent of horologists, Ferdinand Berthoud among them, to London in the hope that Harrison would reveal the Watch’s inner workings. Harrison, understandably wary by this time, shooed the French away, and begged his own countrymen to give him some assurance that no one would pirate his idea. He also asked Parliament for £5,000, to put teeth into their promise of protecting his rights. These negotiations quickly reached an impasse. No money and no information changed hands.

Finally, in March of 1764, William and his friend Thomas Wyatt boarded H.M.S. Tartar and sailed to Barbados with H-4. The Tartar’s captain, Sir John Lindsay, oversaw this first phase of the second trial, and monitored the handling of the Watch on the way to the West Indies. Arriving ashore on May 15, prepared to compare notes with the board-appointed astronomers who had preceded him to the island aboard the Princess Louisa, William found a familiar face. There at the observatory, standing ready to judge the performance of the Watch, was Nathaniel Bliss’s handpicked henchman, none other than the Reverend Nevil Maskelyne.

Maskelyne was undergoing something of a second trial himself, he had complained to the locals. His lunar distance method had clearly shown itself the supreme solution to the longitude problem on the voyage to St. Helena. And this time, en route to Barbados, he boasted, he was sure he’d clinched the case and secured the prize.

When William heard word of these claims, he and Captain Lindsay challenged Maskelyne’s fitness to judge H-4 impartially. Maskelyne was outraged by their accusations. He became huffy, then nervous. In his disquieted condition, he botched the astronomical observations—even though all those present recalled there wasn’t a cloud in the sky.